1. Field of the Invention
This invention relates to a low cost drug delivery system useful in delivering drugs, from pliable plastic containers.
2. Description of the Related Art
Many drugs in the healthcare field are administered to a patient on a continuous basis. Continuous delivery of a drug to a patient was initially achieved by placing a drug delivery bag filled with a drug above the patient and letting gravity force the drug from the bag into the patient. Although this method has proven successful for many applications, its drawbacks included a) an unsteady flow to the patient due to the changing height of the intravenous infusion site relative to the drug bag, b) the awkwardness of requiring the patient to remain below the fluid delivery bag at all times, and c) the constant adjustment of a roller clamp which regulates the flow to the patient. Electromechanical infusion pumps were developed to mitigate these concerns. However, the utility of such pumps was hindered by their bulky size and by their need for a constant source of electricity. These hindrances are especially troublesome in situations where a patient is at home and ambulatory, thus requiring the freedom to move about.
During the past five years, a new style of apparatus has entered the marketplace for controlled delivery of a drug which does not require the use of an electromechanical infusion pump, and thus is suited for the controlled delivery of drugs to patients who are ambulatory. This new style utilizes an inflatable latex rubber balloon housed inside a rigid, clear plastic housing. When the devices are filled with a drug, the latex balloon expands. An administration set is attached to the device and thus acts as the conduit for the drug to the patient. When the balloon is inflated by the drug, the balloon itself becomes the driving force to transfer the drug out of the reservoir to the patient via the drug administration set. Controlled release of the drug at a desired flow rate is achieved by placing an orifice of predetermined diameter in the drug line. These devices generally operated at a relatively high pressures of approximately 10 to 15 psi. Examples of the latex balloon system are disclosed in U.S. Pat. Nos. 4,769,008 and 4,915,693 and European Patent Application 0,426,319 A2.
Although the latex balloon method of drug delivery has certain advantages over the electromechanical infusion pump, the method also has its disadvantages. For example, because the balloon expands in all directions, the shape of the housing enclosing the balloon is round. This round shape does not conform well to the patient when worn in the patient""s pocket. Furthermore, some of the latex balloon style devices require a special machine to fill and pressurize the balloon with a drug. Consequently, the pharmacist must use the special machine to load the device. Thus, there exists the need for a safe, economical drug delivery system which could (a) be inconspicuously and comfortably worn by the patient, (b) allow the pharmacist to fill the drug container without the use of a special pressurizing device, (c) allow the nurse or patient to load the drug container into the pressurizing device, (d) allow for reuse of parts of the system.
The present invention allows the use of standard, rectangular medication bags to be used in a platen pump. By using the standard bags, hospitals do not have to maintain a large inventory of medication bags of differing size and shape.
One aspect of the present invention is an infusion pump for expelling a fluid from a fluid reservoir. The infusion pump comprises a housing having a chamber therein for receiving a fluid reservoir and a first wall for contacting the fluid reservoir. A second wall is movable between a first position distanced from the first wall to form the chamber therebetween, and a second position relatively closer to the first wall. The second wall is moved by a parallelogram linkage. The parallelogram linkage comprises at least one spring for biasing the parallelogram linkage. The movement of the parallelogram linkage causes the second wall to advance toward the first wall. Importantly, the advancement of the second wall provides increased force on the fluid reservoir through the dispensation cycle thereby achieving a constant flow rate.
In another embodiment, an infusion pump comprises a housing having a chamber therein for receiving a fluid reservoir. The pump contains a first wall for contacting the fluid reservoir and a second wall movable between a first position distanced from the first wall to form the chamber therebetween, and a second position relatively closer to the first wall. The pump includes a compression means for moving the second wall, wherein the compression means achieves a substantially constant flow rate from the fluid reservoir by increasing the force applied to the fluid reservoir as the second wall moves toward the second position.
In a further embodiment, an infusion pump for expelling fluid from a fluid bag is provided. The fluid bag has an outlet. The infusion pump includes a generally rectangular base having a non-planar bag-engaging inner surface for supporting the fluid bag. The base has a slot around at least a portion of a periphery thereof. A generally rectangular cover cooperates with the base to define a space in which the bag may be positioned. The cover has a rim extending about at least a portion thereof for mating engagement with the slot of the base, whereby the cover may be selectively connected to the base. A generally rectangular platen is movably connected to the cover and moveable from a first distance above the inner surface of the base to a second distance nearer the inner surface of the base than the first distance. The platen has a bag-engaging surface which is non-planar and complementary to the bag-engaging inner surface of the base. The platen is connected to the cover with a linkage. A first shaft has a first end and a second end and a second shaft has a first end and a second end. A pair of slides are movably mounted along the first and second shafts. A spring is mounted between each end of the ends of the springs and the slides. The linkage comprises a parallelogram linkage formed by four arms, the arms being rotatably connected to the slides and rotatably connected to the platen and the cover. A rod engages the platen and extends through the cover for engagement with a handle, whereby rotation of the handle causes the platen to move upwardly towards the cover, thereby compressing the springs.
In another embodiment, an infusion pump for expelling fluid from a fluid bag having an outlet is provided. The infusion pump includes a generally rectangular base having a non-planar bag-engaging inner surface for supporting the fluid bag. The base also has a slot around at least a portion of a periphery thereof. A generally rectangular cover cooperates with the base to define a space in which the bag may be positioned. The cover has a rim extending about at least a portion thereof for mating engagement with the slot of the base, whereby the cover may be selectively connected to the base. A generally rectangular platen is movably connected to the cover and moveable from a first distance above the inner surface of the base to a second distance nearer the inner surface of the base than the first distance. The platen has a bag-engaging surface which is non-planar and complementary to the bag-engaging inner surface of the base. The platen is connected to the cover with a first and a second linkage. Further, a first shaft having a first end and a second end and a second shaft having a first end and a second end are provided and a first slide and a second slide movably mounted along the first and second shafts. A spring is mounted between each end of the ends of the springs and the slides. Each linkage comprises a parallelogram linkage formed by four arms. A first arm is rotatably connected to the first slide and rotatably connected to the platen. A second arm is rotatably connected to the second slide and rotatably connected to the platen. A third of the arms is rotatably connected to the first slide and the cover. A fourth arm is rotatably connected to the second slide and rotatably connected to the cover. The arms of the first and second linkages are positioned on opposite sides of the slides. A rod engages the platen and extends through the cover for engagement with a handle, whereby rotation of the handle causes the platen to move upwardly towards the cover, thereby compressing the springs.
Further features and advantages of the present invention will become apparent to one of skill in the art from a review of the Detailed Description of Preferred Embodiments which follows, when considered with the attached claims and drawings.